Recent WebKit browsers (I’m looking at Safari 5.0.1 and Chrome 6.0.472.36 beta) now adhere to the CSS3 border-radius spec, so you can drop the -webkit- vendor prefix. But conflict occurs when you use two parameters as the value.

.box {
  -webkit-border-radius: 40px 10px;
     -moz-border-radius: 40px 10px;
          border-radius: 40px 10px;
}

Firefox, Opera, and the latest WebKit browsers (and IE9, I’m guessing) will display a box with the top-left and bottom-right with 40px border-radius, and a top-right and bottom-left with a border-radius of 10px.

But older WebKit browsers will not have the new border-radius rule overwrite the previous -webkit-border-radius, and instead the box with have an eliptical border-radius, the equivalent of border-radius: 40px/10px;.